1.) Field of the Invention
This invention relates to an improved sensor and sensing system for assaying the concentration of an analyte in a solution. More particularly, the sensor and sensing system eliminate interferants by selectively oxidizing the interferants before such interferants interfere substantially with the assay.
2.) Description of the Prior Art
Glucose is typically assayed by detecting the concentration of glucose at enzyme electrodes using glucose oxidase. Because of overlapping oxidation potentials, existing enzyme electrode sensors cannot discriminate between glucose and other electrooxidizable species (hereafter "interferants") such as ascorbate, urate, bilirubin, cysteine, and acetaminophenol. Consequently, these interfering species, and other species which also have overlapping oxidation potentials, prevent the accurate analysis of glucose levels in blood samples.
Persons skilled in the art have searched for ways to prevent the interferants from affecting the accurate analysis of glucose in blood solutions. U.S. Pat. No. 4,098,574 to Dappen appears to disclose that interferants of fluoride ion with glucose analysis performed in integral multilayer elements can be reduced or eliminated by buffering the reagent composition contained therein to a pH between 4.5 and 6.0. U.S. Pat. No. 4,247,297 to Berti et al. appears to claim a test system "highly resistant to interfering reducing substances" through the use of a test means comprising a hydrazone and 8-amino-1-naphthol-5,7-disulfonic acid.
Persons skilled in the art have also attempted to design highly specific sensors, partly in an effort to reduce the effect of interferants. U.S. Pat. No. 4,776,944 to Janata et al. appears to disclose a chemical selective sensor system which utilizes admittance modulation to detect the presence of chemicals in a fluid. Commercial variations of the glucose sensors have also utilized filtering membranes and electrostatic repulsion membranes to inhibit interferants from reaching the analyte sensing layer.
Despite the above described improvements, persons skilled in the art have not yet adequately solved the inaccuracy problems caused by interferants.